1. Field of the Invention
The present invention relates to an optical component consisting of a single crystal element or elements having a property of causing dextrorotation (clockwise rotation) of a plane of polarization of a light beam propagated therethrough, and a single crystal element or elements having a property of causing levorotation (counterclockwise rotation) of the beam polarization plane, or an optical magnetic-field sensor including an optical component consisting of a single crystal element or elements having the properties of causing the dextrorotation of the polarization plane and producing a magnetooptical effect or the Faraday effect, and a single crystal element or elements having the properties of causing levorotation of the polarization plane and producing the magnetooptical effect or the Faraday effect.
2. Discussion of the Prior Art
As one optical component of an optical unit, there is known an optical component of a type which consists of a single crystal element having a property of causing dextrorotation of the plane of polarization of a light beam during propagation of the beam through the element, and a single crystal element having a property of causing levorotation of the polarization plane of the beam. An example of such an optical component is disclosed in laid-open Publication No. 58-140716 of unexamined Japanese Patent Application, which uses a first single crystal of BSO (Bi.sub.12 SiO.sub.20) or BGO (Bi.sub.12 GeO.sub.20) which has a property of causing an incident plane-polarized light beam to undergo dextrorotation of the polarization plane, and a second single crystal of BSO or BGO which has the same effective length as the first single crystal and which has a property of causing the light beam to undergo levorotation of the polarization plane. These first and second single crystals are bonded together in series in a direction of propagation of the light beam through the optical element, so that the properties of causing the dextrorotation and levorotation of the beam polarization plane may be offset or canceled by each other, so as to substantially eliminate an influence of the optical rotatory powers of the light beam while the beam is propagated through the single crystals.
Another type of optical component is disclosed in laid-open Publication No. 61-250572 of unexamined Japanese Patent Application. This optical component uses a first single crystal element having properties of causing the dextrorotation of the polarization plane of a beam and producing a magnetooptical effect or Faraday effect (polarization plane rotation of a beam when passing through the element in a magnetic field), and a second single crystal element having the properties of causing the levorotation of the beam polarization plane and producing the magnetooptical effect or the Faraday effect. These first and second single crystal elements are bonded together in series in the direction of propagation of the light beam. By adjusting the effective lengths of these single crystal elements, the temperature characteristic of the optical rotatory powers of the beam propagated through the elements may be canceled by the temperature characteristic of the magnetooptical effects of the elements, so as to minimize the temperature dependence of the optical component as a whole.
Usually, the intensity of the light beam which has been propagated through or emitted from such an optical component is used as a parameter or variable to be detected. Accordingly, it is desirable to minimize the amount of attenuation of the light while the light is propagated through the optical component (single crystal elements).
In the optical component as disclosed in the above-identified publications (Japanese laid-open publications Nos. 58-140716 and 61-250572), however, a bonding interface between the first and second single crystal elements having different optical properties acts as a reflecting surface since the two elements are disposed in series in the direction of propagation of the light beam, i.e., since the plane of bonding or adjoining interface of the two elements is perpendicular to the beam propagation direction. Consequently, the bonding interface necessarily increases the total number of the surfaces of the optical component (including the end faces of the single crystals) by which a certain portion of the light beam is reflected. Accordingly, the ratio of the portion of the light beam reflected by the optical component, to that of the beam transmitted through the component, is increased. Thus, the light beam is considerably attenuated while it is transmitted through the optical component. Where the optical component is used in an optical sensor whose output is determined by the intensity of the light beam emitted from the optical component, for example, in a magnetic-field sensor (as disclosed in the above-identified publications) for detecting the magnitude of a magnetic field to which the optical component is exposed, the sensing accuracy or sensitivity of the sensor inevitably tends to be lowered due to the attenuation of the light beam during propagation through the optical component. That is, the known optical component or sensor suffers from the relatively low sensitivity or sensing accuracy.
The optical component indicated above is incorporated in an optical unit of an optical device such as a magnetic-field sensor as disclosed in the publications identified above, which optical unit includes other optical components such as a polarizer and an analyzer. The single crystal elements of the optical component in question usually interposed between the polarizer and analyzer generally consist of single crystals each of which exhibits a magnetooptical or Faraday effect in the presence of a magnetic field, as well as exhibits the property of causing dextrorotation or levorotation of the plane of polarization of a light beam in the absence of a magnetic field.
In the optical magnetic-field sensor indicated above, the optical rotatory powers and the magnetooptical effects of the single crystal elements are influenced by or changed with a variation of the operating temperature of the sensor. To reduce the sensing error arising from this temperature variation, it is desirable that the temperature dependence of the rotations of the beam polarization plane be canceled by the temperature dependence of the magnetooptical effects, as proposed in the laid-open Publication No. 61-250572.
As pointed out above, however, the known optical magnetic-field sensor disclosed in the Publication No. 61-250572 suffers from the reflection of a relatively large portion of the incident light beam by the bonding interface of the first and second single crystal elements as well as by the end faces of the elements, because the bonding interface of the two elements having the different optical properties is normal to the direction of propagation of the light beam. Further, the arrangement of the optical sensor in question inherently has a certain slight residual difference in the angle of rotation due to the optical rotatory powers between the first and second single crystal elements. When the relevant optical component and the analyzer are disposed such that the plane of polarization of the light beam emitted from the optical component is rotated by 45.degree. with respect to the plane of incidence of the analyzer about the optical axis of the sensor, the latter plane must be finely adjusted so as to compensate for the residual difference between the angles of rotation of the light polarization plane of the single crystal elements. This complicates the assembling procedure of the optical unit of the sensor.